This invention relates to hydraulic valve lifters in general and more specifically to a hydraulic valve lifter for use in the valve train of internal combustion engines.
In the valve train of an internal combustion engine, a predetermined valve clearance is generally provided to compensate for thermal expansion of various parts in the valve train. However, since excessive lash may be generated due to the valve clearance in the valve train during engine operation, hydraulic valve lifters have been used for automatically taking up the valve clearance in the valve train, thereby preventing possible lash and insuring the proper engagement of the valve face with the corresponding seat.
A conventional hydraulic valve lifter of this type is disclosed, for example, in Japanese patent laid open publication No. 56-132413. FIG. 1 of the present application shows the basic construction of this conventional hydraulic valve lifter which includes a cylindrical first body member 11 in engagement with a cam shaft 12 and a second body member 13 in contact with a valve stem 14. An inner support member 15 is secured on the inner circumferential wall of the first body member 11 and is provided with a frustum or conical portion 16 and a cylindrical portion 17 in which the second body member 13 is slidably mounted. A plunger member 18 is mounted for reciprocation in the second body member 13 and is constantly biased upwardly by means of a spring 19 within the second body member 13. A pressure chamber 20 is defined between the second body member 13 and the plunger member 18 and is normally filled with hydraulic fluid such as lubricating oil. A first reservoir chamber 21 is located in the plunger member 18 and is connected to the pressure chamber 20 through a check valve 22. The reservoir chamber 21 receives a supply of lubricating oil from the engine oil pump through a radial port 23 located in the first body member 11, and oil channel 24 between the first body member 11 and the inner support member 15, and a second reservoir chamber 25 located between the frustum portion 16 and the first body member 11.
When the cam 12 moves to the lowest portion shown in FIG. 1, and downward force is transmitted to the first body member 11. The downward movement of the plunger member 18 is transmitted to the valve stem 14 through the medium of the hydraulic fluid within the pressure chamber 10. As the load of the valve spring 26 increases, the fluid pressure in the pressure chamber 20 will also increase. At this time, a slight leakage of fluid from the pressure chamber 20 occurs through a leakage clearance 27 between the plunger member 18 and the second body member 13 whereby the plunger member 18 is lowered into the second body member 13 to shorten the axial length of the valve lifter assembly 10. When the cam 12 moves upwardly from the position shown in FIG. 1, the first body member 11 is released from the downward force of the cam 12 and the load of the valve spring 26 decreases. Since the volume of the pressure chamber 20 is increased by the action of the spring 19, the fluid pressure in the pressure chamber 20 decreases, thereby permitting the check valve 22 to separate from its valve seat. As a result, the leakage through the clearance 27 is compensated thereby restoring the axial length of the valve lifter assembly 10 to the initial length.
In the conventional valve lifter assembly 10, it is apparent from FIG. 1 that the inner support member 15 secured on the inner circumferential wall of the first body member 11 is provided with the cylindrical portion 17 guiding the second body member 13 and defines the oil channel 24 supplying lubricating oil to the first reservoir chamber 21. Furthermore, the inner support member 15 is provided with the frustum portion or the conical portion 16. Therefore, when air enters into the reservoir chambers 21, 25 from the outside, the air remains above the frustum portion 16 of the inner support member 15 so that the air is not discharged to the outside through the clearance between the sliding surfaces of the cylindrical portion 17 and the second body member 13. Accordingly, since the air is intermixed with the oil in the first reservoir chamber 21, the air may further enter into the pressure chamber 20 with the result that the rigidity of the valve lifter assembly 10 will disappear and a striking sound of the engine valve will be produced. In the situation where the valve lifter 10 is mounted in an engine in an inclined condition with respect thereto, the level at which the air remains in the reservoir chamber 21 is the same level at which the check valve 22 is positioned, making it possible for air to enter into the pressure chamber 20.